U.S. patent number 10,941,070 [Application Number 15/120,003] was granted by the patent office on 2021-03-09 for methods and apparatus for cutting radii in flexible thin glass.
This patent grant is currently assigned to CORNING INCORPORATED. The grantee listed for this patent is Corning Incorporated. Invention is credited to Andrew Stephen Altman, Carlton Wesley Cole, Todd Benson Fleming, Anping Liu, James Joseph Watkins.
United States Patent |
10,941,070 |
Altman , et al. |
March 9, 2021 |
Methods and apparatus for cutting radii in flexible thin glass
Abstract
Methods and apparatus provide for: cutting a thin glass sheet
along a curved cutting line, where the curve is divided into a
plurality of line segments; applying a laser beam and continuously
moving the laser beam along the cutting line; applying a cooling
fluid simultaneously with the application of the laser beam in
order to propagate a fracture in the glass sheet along the cutting
line; and varying one or more cutting parameters as the laser beam
moves from one of the plurality of line segments to a next one of
the plurality of line segments, wherein the one or more cutting
parameters include at least one of: (i) a power of the laser beam,
(ii) a speed of the movement, (iii) a pressure of the cooling
fluid, and (iv) a flow rate of the cooling fluid.
Inventors: |
Altman; Andrew Stephen
(Westfield, PA), Cole; Carlton Wesley (Elmira, NY),
Fleming; Todd Benson (Elkland, PA), Liu; Anping
(Horseheads, NY), Watkins; James Joseph (Corning, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
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Assignee: |
CORNING INCORPORATED (Corning,
NY)
|
Family
ID: |
1000005409017 |
Appl.
No.: |
15/120,003 |
Filed: |
February 17, 2015 |
PCT
Filed: |
February 17, 2015 |
PCT No.: |
PCT/US2015/016096 |
371(c)(1),(2),(4) Date: |
August 18, 2016 |
PCT
Pub. No.: |
WO2015/126805 |
PCT
Pub. Date: |
August 27, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170050877 A1 |
Feb 23, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61942309 |
Feb 20, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B
33/0222 (20130101); B23K 26/53 (20151001); C03B
33/04 (20130101); B23K 26/14 (20130101); C03B
33/091 (20130101); B23K 2103/54 (20180801); Y02P
40/57 (20151101) |
Current International
Class: |
C03B
33/09 (20060101); B23K 26/14 (20140101); C03B
33/04 (20060101); C03B 33/02 (20060101); B23K
26/53 (20140101) |
References Cited
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Other References
EP15751546.1 Search Report dated Dec. 8, 2017, European Patent
Office, 5 pgs. cited by applicant .
International Search Report and Written Opinion of the
International Searching Authority; PCT/US2015/016096; dated May 29,
2015; 10 Pages; Korean Intellectual Property Office. cited by
applicant .
Lumley, R. M., Controlled Separation of Brittle Materials using a
Laser, Am. Ceram. Soc. Bull., 48 (9), pp. 850-854, 1969. cited by
applicant .
English Translation of TW104105649 Summary of Official Letter and
Search Report dated Jun. 4, 2018, Taiwan Patent Office,2 Pgs. cited
by applicant .
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.
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.
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cited by applicant.
|
Primary Examiner: Dehghan; Queenie S
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority under 35 U.S.C.
.sctn. 371 of International Patent Application Serial No.
PCT/US15/16096, filed on Feb. 17, 2015, which in turn, claims the
benefit of priority of U.S. Provisional Patent Application Ser. No.
61/942,309 filed on Feb. 20, 2014, the contents of each of which
are relied upon and incorporated herein by reference in their
entireties.
Claims
The invention claimed is:
1. A method, comprising: supporting a source glass sheet of about
0.2 mm or less in thickness; defining a cutting line having at
least one non-straight portion of a radius of less than about 20
mm, where the cutting line defines a desired shape of a glass
substrate; dividing the non-straight portion of the cutting line
into a plurality of sequential line segments; initiating a flaw in
the glass sheet; applying a laser beam to the glass sheet starting
at the flaw and continuously moving the laser beam and the glass
sheet relative to one another along the cutting line to elevate a
temperature of the glass sheet at the cutting line; applying a
cooling fluid simultaneously with the application of the laser
beam, such that the cooling fluid at least reduces the temperature
of the glass sheet in order to propagate a fracture in the glass
sheet along the cutting line; varying a speed of movement of the
laser beam as the laser beam moves from one line segment to a next
line segment such that the speed is higher, by at least about 10%
when the cutting line is straight as compared with when the cutting
line is curved; and separating waste glass from the glass sheet to
obtain the glass substrate of the desired shape.
2. The method of claim 1, wherein the laser beam is substantially
circular having a diameter of between about 1 mm to about 5 mm, or
the laser beam is moderately non-circular having an aspect ratio of
less than about 2 and a diameter of less than about 5 mm.
3. The method of claim 1, wherein the cooling fluid is directed
annularly about the laser beam toward the glass sheet.
4. The method of claim 1 wherein the resulting glass substrate has
a non-straight edge portion with an edge strength of greater than
about 150 MPa, and the at least one non-straight edge portion is
not strengthened by polishing.
5. The method of claim 1 wherein the resulting glass substrate has
a non-straight edge portion with an edge strength of the at least
one non-straight edge portion is greater than about 300 MPa.
6. The method of claim 1 wherein the resulting glass substrate has
a non-straight edge portion with an edge strength of the at least
one non-straight edge portion is greater than about 400 MPa.
7. The method of claim 1 wherein the resulting glass substrate has
a hackle size is less than about 50% of the glass thickness.
8. The method of claim 1, further comprising varying a power level
of the laser beam as the laser beam moves from one line segment to
a line segment such that the power level is higher, by at least
about 10% when the cutting line is straight as compared with when
the cutting line is curved.
9. A method, comprising: supporting a source glass sheet of about
0.2 mm or less in thickness; defining a cutting line having at
least one non-straight portion of a radius of less than about 20
mm, where the cutting line defines a desired shape of a glass
substrate; dividing the non-straight portion of the cutting line
into a plurality of sequential line segments; initiating a flaw in
the glass sheet; applying a laser beam to the glass sheet starting
at the flaw and continuously moving the laser beam and the glass
sheet relative to one another along the cutting line to elevate a
temperature of the glass sheet at the cutting line; applying a
cooling fluid simultaneously with the application of the laser
beam, such that the cooling fluid at least reduces the temperature
of the glass sheet in order to propagate a fracture in the glass
sheet along the cutting line; varying a speed of the movement of
the laser beam as the laser beam moves from one line segment to a
next line segment, such that the power and/or speed varies by at
least about 2% between all subsequent line segments; and separating
waste glass from the glass sheet to obtain the glass substrate of
the desired shape.
10. The method of claim 9, wherein the laser beam is substantially
circular having a diameter of between about 1 mm to about 5 mm, or
the laser beam is moderately non-circular having an aspect ratio of
less than about 2 and a diameter of less than about 5 mm.
11. The method of claim 9, wherein the resulting glass substrate
has a non-straight edge portion with an edge strength of greater
than about 150 MPa, and the at least one non-straight edge portion
is not strengthened by polishing.
12. The method of claim 9 wherein the resulting glass substrate has
a non-straight edge portion with an edge strength of the at least
one non-straight edge portion is greater than about 300 MPa.
13. The method of claim 9 wherein the resulting glass substrate has
a non-straight edge portion with an edge strength of the at least
one non-straight edge portion is greater than about 400 MPa.
14. The method of claim 9 wherein the resulting glass substrate has
a hackle size is less than about 50% of the glass thickness.
15. The method of claim 9, wherein the cooling fluid is directed
annularly about the laser beam toward the glass sheet.
Description
BACKGROUND
The present disclosure relates to methods and apparatus for cutting
radii into flexible thin glass.
Conventional manufacturing techniques for cutting flexible plastic
substrates have been developed, where the plastic substrates employ
a plastic base material laminated with one or more polymer films.
These laminated structures are commonly used in flexible packaging
associated with photovoltaic (PV) devices, organic light emitting
diodes (OLED), liquid crystal displays (LCD) and patterned thin
film transistor (TFT) electronics, mostly because of their
relatively low cost and demonstrable performance.
Although the aforementioned flexible plastic substrates have come
into wide use, they nevertheless exhibit poor characteristics in
connection with at least providing a moisture barrier and providing
very thin structures (indeed, the structures are relatively thick
owing to the properties of plastic materials).
Accordingly, there are needs in the art for new methods and
apparatus for fabricating a flexible substrate for use in, for
example, PV devices, OLED devices, LCDs, TFT electronics, etc.,
particularly where the substrate is to provide a moisture barrier
and the substrate is to be formed into a shape having at least one
radius at a corner.
SUMMARY
The present disclosure relates to employing a relatively thin,
flexible, glass sheet (on the order of less than about 0.2 mm) and
cutting the glass sheet into a shape having at least one radius
(such as a free-form shape).
Flexible glass substrates offer several technical advantages over
the existing flexible plastic substrate in use today. One technical
advantage is the ability of the glass substrate to serve as good
moisture or gas barrier, which is a primary degradation mechanism
in outdoor applications of electronic devices. Another advantage is
the potential for the flexible glass substrate to reduce the
overall package size (thickness) and weight of a final product
through the reduction or elimination of one or more package
substrate layers. As the demand for thinner, flexible substrates
(on the order of less than about 0.2 mm thick) increases in the
electronic display industry, manufacturers are facing a number of
challenges for providing suitable flexible substrates.
Although techniques exist for the continuous cutting of ultra-thin
glass web, for example glass web measuring less than about 0.2 mm
thick, such techniques are generally directed to cutting the glass
web into straight strips of particular widths.
A significant challenge in fabricating flexible glass substrates
for PV devices, OLED devices, LCDs, TFT electronics, etc., is
cutting a source of relatively large, thin glass sheet into smaller
discrete substrates of various dimensions and shapes with tight
dimensional tolerances, good edge quality, and high edge strength.
Indeed, a desired manufacturing requirement is to cut glass parts
off a source glass sheet continuously, without interruption of the
cutting line, where the cutting line includes at least some round
sections (e.g., at least one rounded corner). Although existing
mechanical techniques for continuous cutting of irregular (free
form) shapes provide for scoring (with a score wheel) and
mechanical breaking (or snapping), the edge quality and strength
achieved by such mechanical techniques are not sufficient for many
applications where precision and/or high edge strength are
required. Indeed, the mechanical scoring and breaking approach
generates glass particles and manufacturing failures, which
decreases the process yield and increases manufacturing cycle
time.
In accordance with one or more embodiments herein, a laser cutting
technique is employed to cut a thin glass sheet into a free form
shape having at least one rounded corner or rounded portion. Glass
cutting techniques using a laser are known, however, such
techniques are generally directed to cutting glass sheets having
thicknesses of at least 0.4 mm and thicker--and the technique
involves laser scoring followed by mechanical breaking (score and
snap). The cutting of thin flexible glass with thicknesses of less
than about 0.2 mm (and even as low as tens of um in a roll format)
presents significant challenges, especially when tight dimensional
tolerances and high edge strength are required manufacturing
objectives. The conventional laser score and mechanical break
process is nearly impossible to reliably employ with glass sheet
thicknesses of less than about 0.2 mm. Indeed, due to the
relatively thin profile of a glass sheet of less than about 0.2 mm,
the stiffness of the sheet is very low (i.e., the sheet is
flexible), and the laser score and snap cutting process is easily
adversely affected by thermal buckling, mechanical deformation, air
flows, internal stress, glass warpage, and many other factors. In
order to remove edge macro-cracks and improve edge strength after a
conventional cutting process, the cut edges must be fine polished
to avoid further cracks and failure. This in turn, increases
production costs and reduces yields.
In contrast, the embodiments herein present laser cutting
techniques resulting in free form shapes of thin flexible glass,
whereby one-step, continuous, full separation process in which a
free form shape is obtained from a source glass sheet. Importantly,
the cutting technique results in high edge strength (at least
greater than about 150 MPa) even along the radii.
The novel methodology and apparatus provides for the propagation of
an initiation flaw, for example a crack in the source glass sheet,
via a laser (for example a CO2 laser beam) and simultaneous
provision of a cooling fluid (for example a gas, such as air). The
methodology and apparatus is applicable to thin and ultra-thin
glass sheets with thicknesses of less than about 0.2 mm, for
example between about 0.02 mm to 0.2 mm, between about 0.05 mm to
0.2 mm, and/or between about 0.1 mm to 0.2 mm. Notably, cutting of
thinner glass sheets is possible, and the cutting of thicker glass
sheets (i.e., greater than about 0.2 mm) is also possible.
Advantages of the embodiments herein include: (i) reducing crack
propagation defects (such as hackle and chipping) and thereby
reducing particle generation; (ii) reducing surface scratches,
improving edge strength, and reducing surface roughness (due to the
one-step, touch-free process); (iii) increasing production yields
(elimination of mechanical snapping and resultant unwanted cracks
and breaks); (iv) optimizing free-form cutting, including curvature
radii as low as about 2 mm; (v) increasing the strength of the
glass substrate (due to the addition of at least one rounded edge
to the structure, as compared to scribed glass having sharp edges
that are easily chipped); (vi) eliminating the need for finishing
(grinding and polishing); (vii) lowering production costs; (viii)
increasing the quality (such as increasing strength) of the cut
edge; (ix) increasing the control of the cutting process (due to
thermally controlled crack propagation, as compared to scored
cracks, which are very difficult to control with thin glass); (x)
improving process capabilities (such as improvement in adjustments
to glass thickness differences in thin glass (due to the use of
laser separation, as compared to scribing which only adjusts well
for greater than about 0.5 mm thicknesses, but does not adjust well
to thickness differences experienced in glass of less than about
0.5 mm thickness); (xi) simplifying the cutting equipment (as the
laser equipment may be readily available from commercial vendors);
(xii) improving cutting options (for example, permitting the
initiation of the cut anywhere on the source glass sheet, not just
from an edge); (xiii) improving cutting results, for example
permitting complete separation from the source glass sheet upon
completion of the laser cut (as opposed to scoring, which requires
one or more intermediate steps as waste sections of the source
glass sheet are cracked off from the glass substrate, thereby
resulting in added stress in the glass); (ixx) reducing and/or
eliminating edge contamination (as compared to mechanical scoring,
which can embed contaminates into the glass edge and/or onto the
glass surface); (xx) improving cut precision and consistency; and
(xxi) eliminating lateral cracks (due to the laser cut edge
increasing the part overall component strength and life expectancy,
thereby satisfying a need in the art).
Other aspects, features, and advantages will be apparent to one
skilled in the art from the description herein taken in conjunction
with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
For the purposes of illustration, there are forms shown in the
drawings that are presently preferred, it being understood,
however, that the embodiments disclosed and described herein are
not limited to the precise arrangements and instrumentalities
shown.
FIG. 1 is top view of a thin, glass substrate produced using one or
more cutting methodologies and apparatus disclosed herein;
FIG. 2 is a top view of a source glass sheet from which the glass
substrate of FIG. 1 may be produced;
FIG. 3 is a schematic illustration of an apparatus that may be used
to cut the glass substrate from the glass sheet;
FIGS. 4A-4B are digital images of a top view and side view,
respectively, of a cut edge of a given radius using a conventional
laser cutting methodology;
FIGS. 5A-5B are digital images of a top view and side view,
respectively, of a cut edge of a given radius using the cutting
methodology of one or more embodiments herein;
FIGS. 6A-6B are schematic illustrations of a front view and a side
view, respectively, of a set up for testing the edge strength of a
cut edge (having a radius) of a glass substrate;
FIG. 7 is a digital image of a cut edge of a glass substrate, which
shows an example of the mirror finish radius resulting from the
test set up of FIGS. 6A-6B; and
FIG. 8 is a Weibull plot of edge strength (of edges with radii)
indicating very high edge strength using the methodologies of one
or more embodiments herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the drawings wherein like numerals indicate like
elements there is shown in FIG. 1 a top view of a thin, glass
substrate 10 produced using one or more cutting methodologies and
apparatus disclosed herein. A number of characteristics of the
glass substrate 10 are of importance when considering the
disclosure herein. First, the glass substrate 10 (and the source
glass sheet from which it is cut) is thin and/or ultra-thin, with a
thickness of less than about 0.2 mm, for example between about 0.01
mm to 0.2 mm, between about 0.05 mm to 0.2 mm, and/or between about
0.1 mm to about 0.2 mm. While these thicknesses are considered
preferable, the glass substrate 10 may be thinner and/or thicker
than the ranges mentioned. Second, the glass substrate 10 is
considered a free form shape, for example having at least one
curved portion, having one or more radii of curvature anywhere from
a minimum of about 2 mm up to about 20 mm. For example, the glass
substrate 10 is shown with four rounded corners, although any other
shape may be employed, for example having a mix of rounded corners,
sharp corners, straight beveled corners, etc. Third, the edge
strength of the curved portions are very high, such as greater than
about 150 MPa, greater than about 200 MPa, greater than about 300
MPa, and/or greater than about 400 MPa.
Reference is now made to FIG. 2, which is a top view of a source
glass sheet 20 from which the glass substrate 10 of FIG. 1 may be
produced. The novel methodology and apparatus disclosed herein
provides for cutting the glass substrate 10 via propagation of an
initiation flaw, for example a crack in the source glass sheet,
using a laser (for example a CO2 laser beam) and simultaneous
provision of a cooling fluid (for example a gas, for example air).
In general, this arrangement results in the controlled propagation
of the crack in the source glass sheet 20 along a desired cutting
line in order to separate the glass substrate 10 from the glass
sheet 20. A more detailed discussion of the methodology and
apparatus for carrying out the initiation, propagation, and
termination of the crack is provided later in this description.
As an initial phase of the process, the source glass sheet 20 (of
the aforementioned thickness) is supported on a suitable support
structure (which will be discussed in more detail later herein) and
a free form cutting line (the dashed line in FIG. 2) is defined
that establishes a closed pattern, where the cutting line
circumscribes the desired final shape of the glass substrate 10.
Those skilled in the art will appreciate that the specific shape of
the free-form cutting line is highly dependent on the specific,
intended application for the glass substrate 10. For example,
although the illustrated cutting line is a closed-curve, such need
not be the case. Indeed, an alternative cutting line may include
one or more curved sections and one or more other sections that
include some of original edge portions of the glass sheet 20. In
such case, the cutting line may intersect one or more of the
original edge portions of the glass sheet 20, whereby the glass
substrate 10 may include such edge portions.
An important aspect in connection with defining the cutting line is
illustrated in the expanded view of one of the rounded portions 12
thereof. In particular, the non-straight, rounded portion 12 has a
radius of less than about 20 mm (such as between about 1 mm and
about 20 mm), and the rounded portion 12 is divided into a
plurality of sequential line segments 14, 16, 18, etc. The line
segments 14, 16, 18 may be of the same length or of differing
lengths. As will be discussed in greater detail later herein, these
line segments 14, 16, 18, represent portions of the cutting line in
which one or more cutting parameters are varied as the laser beam
moves from one of the line segments to a next one of the line
segments.
There are a number of options for the start and/or finish of the
cutting line. For example, one option is that the start and finish
of the cutting line are co-incident, whereby the cutting line is
entirely coincident with the desired contour of the glass substrate
10. Alternatively, the start of the cutting line may be at a
different point as compared to the finish of the cutting line. For
example, the start and/or finish of the cutting line may be at
respective edges of the glass sheet 20 (which are not coincident
with the cutting line). An initial crack (or fracture, or
initiation flaw) is provided at the start of the cutting line, in
particular over a small length (e.g., about 5 mm to 10 mm long) on
the glass sheet 20. Subsequently, the initial crack is lengthened
and propagated using the aforementioned laser cutting technique. In
general, the glass sheet 20 is scored at the initial crack using a
mechanical scoring device, for example a score wheel, or via a
laser based crack initiation technique. In order to appreciate the
significance of the crack initiation and subsequent propagation, a
more detailed discussion of the laser cutting technique will first
be provided.
The laser beam is used to heat the glass sheet 20 in a localized
area and a source of cooling fluid is used to rapidly cool that
area in order to create transient tensile stress via the resultant
temperature gradient. The aforementioned initial crack is created
by introducing a small initial flaw on the surface of the glass
sheet 20, which is then transformed into a vent (the crack)
propagated by heating the localized zone via the laser and cooling
that zone via quenching action produced by the cooling fluid. The
tensile stress, .sigma., produced during the process is
proportional to .alpha.*E*.DELTA.T, where .alpha. is a linear
thermal expansion coefficient of the glass sheet 20, E is a modulus
of elasticity of the glass sheet 20, and .DELTA.T is a temperature
difference on the surface of the glass sheet 20 produced by the
heating (from the laser) the cooling (from the fluid). The tensile
stress is controlled in order to be higher than the molecular bonds
of the glass sheet 20. For a given .alpha.*E tensile stress,
.sigma. can be increased by heating the glass sheet 20 to a higher
temperature via the laser. However, overheating the glass sheet 20
(above its strain point) will cause an ablation and irreversible
high residual stress, which deteriorates the quality of the cut
edge and reduces edge strength. The described method uses full body
glass separation (cutting), where the vent depth is equal to the
thickness of the glass.
Reference is now made to FIG. 2 and FIG. 3, the latter figure being
a schematic illustration of an apparatus 100 that may be used to
cut the glass substrate 10 from the glass sheet 20. The glass sheet
20 may be supported using a support structure 102 (which will be
described in greater detail later herein). By way of example, the
laser beam 60 may be implemented using a source 64 of laser energy,
folding optics 66, and focusing optics 68. Those skilled in the art
will appreciate that many variations in the specific of the optics
implementation exist. Application of the laser beam 60 to the glass
sheet 20 starting at the initial crack initiates propagation of the
crack. Continuous moving of the laser beam 60 relative to the glass
sheet 20 along the cutting line elevates the temperature of the
glass sheet 20 at the cutting line. Simultaneously, the cooling
fluid 62 is applied relative to the laser beam 60 (via a nozzle
70), such that the cooling fluid 62 causes a temperature
differential in the glass sheet 20 in order to induce the
aforementioned tensile stress and propagate the crack (i.e., a
fracture or vent) in the glass sheet 20 along the cutting line.
Movement of the laser beam 60 and nozzle 70 relative to the glass
sheet 20 may be achieved through any of the known conveyance
mechanisms.
It has been discovered that curved, free form laser cutting may be
achieved using a laser beam 60 of a substantially round shape
surrounded by an annular, circular, ring-shaped coolant zone 62
(achieved using the coolant source nozzle 70). The circular laser
beam 60, together with the annular coolant zone 62 does not exhibit
any predefined or inherent orientation (as is the case with
significantly elliptical laser beams), and therefore can be used to
propagate the crack in any direction (without having to use any
complex beam shaping techniques or provide any additional motion
axes for movement of the nozzle 70). While nozzles that produce
annular, ring-shaped fluid flow in laser cutting applications are
known, they have heretofore been applied to straight laser cutting
methodologies or to cutting thicker glass via the score and break
method (where a partial vent is created followed by mechanical
break). In contrast, the embodiments herein employ a ring nozzle 70
for a full body separation (or cut) of a thin glass sheet 20.
Additionally, while small diameter laser beams are also known for
free form laser cutting, the embodiments herein apply a combination
of the nozzle 70 for annular fluid flow (in stationary relationship
to the laser beam 60), and other cutting variables to achieve
superior edge characteristics, including high edge strength. For a
small, substantially round beam, the diameter of the laser beam 60
may be about 1-5 mm, preferably between about 2-4 mm. For a small,
moderately non-circular beam, an aspect ratio of the laser beam 60
may be less than about 2, and a diameter of the laser beam 60 may
be less than about 5 mm. The laser beam 60 may be of a Gaussian,
non-Gaussian, or flat-top beam power distribution.
The source of laser power 64 may be implemented using CO2 laser
mechanisms, however, other implementations are possible, for
example a fiber laser, an Nd:YAG laser, or other laser systems. A
carbon dioxide laser operates at the wavelength of 10.6 .mu.m. In
general, using a laser beam 60 having the diameters disclosed
herein allows certain advantageous effects: (i) minimization of
edge imperfections associated with the crack initiation (the
smaller the beam diameter, the smaller the unstable crack
propagation zone); (ii) ability to propagate the crack nearly to
the edge of the glass sheet 20 (i.e., to permit termination of the
crack in proximity to the edge of the glass sheet 20, thereby
avoiding a hook at the end of the cut; and (iii) maintaining
reasonably high cutting speed even with a small diameter beam,
resulting in relatively short processing time and high
throughput.
As noted above, a very desirable edge characteristic for the glass
substrate 10 is high edge strength, on the straight portions as
well as on the curved portions. For thin glass substrates (less
than about 0.2 mm) high edge strength of greater than about 150
MPa, greater than about 200 MPa, greater than about 300 MPa, and/or
greater than about 400 MPa are not conventionally achievable,
especially on the curved edges. In order to achieve the
aforementioned high edge strength, one or more of the cutting
parameters are varied as the laser beam moves from one of the
plurality of line segments 14, 16, 18, etc. to a next one of the
plurality of line segments. These cutting parameters may include at
least one of: (i) a power of the laser beam, (ii) a speed of the
movement, and (iii) at least one of a pressure and flow rate of the
cooling fluid.
These cutting parameters may be controlled via a controller 80, for
example implemented using a computer system employing a
microprocessor, memory, and software code. The controller commands
certain characteristics of the laser source 64, the nozzle 70,
and/or the support structure 102. For example, the controller 80
may operate to vary the power of the laser beam 60 such that the
power level is different in at least one of the line segments 14,
16, 18, etc. as compared to others of the line segments. By way of
example, the definition of "different" as concerns the power level
may be at least about 2%, at least about 5%, and/or at least about
10%. In another embodiment, the controller 80 may operate to vary
the power of the laser beam 60 such that the power level is
different in all of the line segments 14, 16, 18, etc. Additionally
and/or alternatively, the controller 80 may operate to vary the
speed of the movement of the laser beam 60 relative to the glass
sheet 20 such that the speed is different in at least one of the
line segments 14, 16, 18, etc. as compared to others of the line
segments. By way of example, the definition of "different" as
concerns the speed may be at least about 2%, at least about 5%,
and/or at least about 10%. In another embodiment, the controller 80
may operate to vary the speed of the movement of the laser beam 60
relative to the glass sheet 20 such that the speed is different in
all of the line segments 14, 16, 18, etc. Additionally and/or
alternatively, the controller 80 may operate to vary at least one
of the pressure and flow rate of the cooling fluid 62 such that at
least one of the pressure and flow rate are different in at least
one of the line segments 14, 16, 18, etc. as compared to others of
the line segments. By way of example, the definition of "different"
as concerns the flow rate may be at least about 2%, at least about
5%, and/or at least about 10%. In another embodiment, the
controller 80 may operate to vary at least one of the pressure and
flow rate of the cooling fluid 62 such that at least one of the
pressure and flow rate are different in all of the line segments
14, 16, 18, etc. Additionally and/or alternatively, the controller
80 may operate to vary a supply of air pressure and/or flow of a
support fluid from the support structure 102, which adjusts a fly
height of the glass sheet 20 above the support structure 102, as
the laser beam 60 moves through at least one of the line segments
14, 16, 18, etc. as compared to others of the line segments.
The controller 80 operates to vary the cutting parameters through
the line segments 14, 16, 18 in order to control the temperature
and stresses within the glass sheet 20 as the crack is propagated
along the cutting line. The variability of the cutting parameters
results in improvements in the edge characteristics of the cut
edge, including edge strength, shear, compression, twist hackle,
etc. For example, reference is made to FIGS. 4A-4B, which are
digital images of a top view and a side view, respectively, of a
cut edge of a given radius (less than about 20 mm) of a thin glass
substrate (about 0.2 mm). Notably, the cut edge was produced
without varying the cutting parameters through any line segments of
the cutting line as the laser beam 60 traversed the rounded
portion. Consequently, a number of undesirable edge characteristics
are evident, including large shear, large compression, large twist
hackle, and evidence of an arrest feature 92, where the illustrated
dimension is about 105 um. In comparison, reference is made to
FIGS. 5A-5B, which are digital images of a top view and a side
view, respectively, of a cut edge of a given radius (less than
about 20 mm) of a thin glass substrate (about 0.2 mm). Notably, the
cut edge was produced by varying the cutting parameters through one
or more of the line segments of the cutting line as the laser beam
60 traversed the rounded portion. Consequently, a number of
desirable edge characteristics are evident, including low shear,
low compression, low twist hackle, and no evidence of any arrest
features, where the illustrated dimension is about 114.08 um.
Another important set of parameters in connection with achieving
satisfactory cut edge quality on the finished glass substrate 10 is
providing the functions of transporting the glass sheet 20 (into
and out of the cutting zone of the apparatus 100) and holding the
glass sheet 20 during the cutting process. Assuming that the
support structure 102 will be used for transportation, scoring, and
laser cutting (which is a desirable combination), then the surface
properties of the support structure 102 (especially the surface
underneath the glass sheet 20), and the mechanisms contributing to
the support of the glass sheet 20 during cutting are important for
cutting thin flexible glass of the thicknesses contemplated herein.
In order to use a mechanical scoring mechanism for crack
initiation, the hardness of the surface of the support structure
102 should be relatively hard to avoid flexing. In addition, the
surface of the support structure 102 should be able to withstand
relatively high temperatures generated by the laser beam 60. In
order to move the glass sheet 20 into position for scoring, laser
cutting, and then moving the glass substrate 10 (after the cutting
process is complete) an air bearing mechanism is provided in the
support structure 102. The air bearing may be achieved via a porous
surface of the support structure 102, where the table provides a
variable air-bearing mode (variability of bearing fluid pressure
and/or flow rate). The support bearing fluid of the air bearing is
delivered from the surface of the support structure 102 by way of
the porosity of the surface and a source of fluid of varying
pressure and flow (not shown). The air bearing mode operates to
bias the glass sheet 20 away from the surface of the table of the
support structure 102 as the laser beam 60 elevates the temperature
of the glass sheet 20 and the cooling fluid 62 is directed in
opposing fashion to the support fluid.
Reference is now made to FIGS. 6A-6B, which are schematic
illustrations of a front view and a side view, respectively, of a
set up for testing the edge strength of a glass substrate 10 using
a novel two-point bend methodology. Conventional two-point testing
methodologies operate to test the edge strength of a straight edge.
The test set up illustrated in FIGS. 6A-6B, however, operates to
test the edge strength of a rounded edge 12 (e.g., having a radius
less than about 20 mm). The test set up includes an upper platen
202 and a lower platen 204, whereby the glass substrate 10 is
disposed between the platens 202, 204. In the illustrated example,
the glass substrate 10 includes symmetrical rounded portions on the
lateral sides thereof as well as substantially straight upper and
lower edges, which engage the upper and lower platens 202, 204. As
best seen in FIG. 6B, the upper and lower platens 202, 204 are
moved toward one another in order to flex the glass substrate 10
and present a large stress to the apexes of the rounded portion 12
of the glass substrate 10. The platens 202, 204 are advanced until
the glass substrate 10 breaks.
Next, the break point is identified by examining the fractured edge
of the rounded portion 12. For example, as shown in FIG. 7, the
mirror-finish radius of the rounded portion 12 may be examined
using a suitable inspection apparatus. This entails employing some
methodology (conventional or otherwise) for estimating the fracture
stress of glass. For example, the results in FIG. 7 were obtained
using microscopy, whereby a length of about 36 um was measured
between the hash marks, i.e., the mirror-radius length used in
determining the fracture stress for the samples. Those skilled in
the art will appreciate the steps in such a process based on known
technologies.
Using the above testing setup, a number of glass substrate 10
samples were tested. The glass substrate samples were prepared by
cutting glass sheets of 130 .mu.m thickness using the cutting
process discussed above. In the straight sections of the cutting
line, the cutting parameters included: (i) a laser power of 3.8
watts, (ii) a speed of 860 mm/m, and (iii) an nozzle air flow of
100 l/m. As discussed above, in the curved portions of the cutting
line, one or more of the cutting parameters are varied as the laser
beam moves from one of the plurality of line segments 14, 16, 18 to
a next one of the plurality of line segments. In particular, in
segment 14 the cutting parameters included: (i) a laser power of
3.0 watts, (ii) a speed of 300 mm/m, and (iii) an nozzle air flow
of 100 l/m. In segment 16 the cutting parameters included: (i) a
laser power of 3.0 watts, (ii) a speed of 350 mm/m, and (iii) an
nozzle air flow of 100 l/m. In segment 18 the cutting parameters
included: (i) a laser power of 3.0 watts, (ii) a speed of 325 mm/m,
and (iii) an nozzle air flow of 100 l/m.
With reference to FIG. 8, the resulting test data are presented on
a Weibull plot (with failure probability along the Y-axis and
maximum bend stress in MPa along the X-axis). The plot shows the
fracture stress in MPa and the data points reveal that for the
samples tested, the edge strength of the rounded portions were
between 100 to 700 MPa. Further, samples having hackle of greater
than about 50% of the glass thickness were noted as being
undesirable and indicative of a cutting process in need of
adjustment.
Although the disclosure herein has been described with reference to
particular embodiments, it is to be understood that these
embodiments are merely illustrative of the principles and
applications of the embodiments herein. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
application. For example, various features of the invention may be
combined according to the following aspects.
According to a first aspect, there is provided a method,
comprising:
supporting a source glass sheet of about 0.2 mm or less in
thickness;
defining a cutting line having at least one non-straight portion of
a radius of less than about 20 mm, where the cutting line defines a
desired shape of a glass substrate;
dividing the non-straight portion of the cutting line into a
plurality of sequential line segments;
initiating a flaw in the glass sheet;
applying a laser beam to the glass sheet starting at the flaw and
continuously moving the laser beam and the glass sheet relative to
one another along the cutting line to elevate a temperature of the
glass sheet at the cutting line;
applying a cooling fluid simultaneously with the application of the
laser beam, such that the cooling fluid at least reduces the
temperature of the glass sheet in order to propagate a fracture in
the glass sheet along the cutting line;
varying one or more cutting parameters as the laser beam moves from
one of the plurality of line segments to a next one of the
plurality of line segments, wherein the one or more cutting
parameters include at least one of: (i) a power of the laser beam,
(ii) a speed of the movement, (iii) a pressure of the cooling
fluid, and (iv) a flow rate of the cooling fluid; and
separating waste glass from the glass sheet to obtain the glass
substrate of the desired shape.
According to a second aspect, there is provided the method of
aspect 1, wherein at least one of:
the laser beam is substantially circular having a diameter of the
laser beam is one of: (i) between about 1 mm to about 5 mm, and
(ii) between about 2 mm to about 4 mm; and
the laser beam is moderately non-circular having an aspect ratio of
less than about 2 and a diameter of less than about 5 mm.
According to a third aspect, there is provided the method of aspect
1 or aspect 2, further comprising varying the power of the laser
beam such that the power level is different, by one of: at least
about 2%, at least about 5%, and at least about 10%, in at least
one of the line segments as compared to others of the line
segments.
According to a fourth aspect, there is provided the method of
aspect 3, further comprising varying the power level of the laser
beam such that the power level is different, by one of: at least
about 2%, at least about 5%, and at least about 10%, in all of the
line segments.
According to a fifth aspect, there is provided the method of any
one of aspects 1-4, further comprising varying a power level of the
laser beam such that the power level is higher, by one of: at least
about 2%, at least about 5%, and at least about 10%, when the
cutting line is straight as compared with when the cutting line is
curved.
According to a sixth aspect, there is provided the method of any
one of aspects 1-5, further comprising varying the speed of the
movement of the laser beam relative to the glass sheet such that
the speed is different, by one of at least about 2%, at least about
5%, and at least about 10%, in at least one of the line segments as
compared to others of the line segments.
According to a seventh aspect, there is provided the method of
aspect 6, further comprising varying the speed of the movement of
the laser beam relative to the glass sheet such that the speed is
different, by one of: at least about 2%, at least about 5%, and at
least about 10%, in all of the line segments.
According to an eighth aspect, there is provided the method of any
one of aspects 1-7, further comprising varying a speed of the
movement of the laser beam relative to the glass sheet such that
the speed is higher, by one of: at least about 2%, at least about
5%, and at least about 10%, when the cutting line is straight as
compared with when the cutting line is curved.
According to a ninth aspect, there is provided the method of any
one of aspects 1-8, further comprising varying at least one of the
pressure and flow rate of the cooling fluid such that at least one
of the pressure and flow rate are different, by one of: at least
about 2%, at least about 5%, and at least about 10%, in at least
one of the line segments as compared to others of the line
segments.
According to a tenth aspect, there is provided the method of aspect
9, further comprising varying at least one of the pressure and flow
rate of the cooling fluid such that at least one of the pressure
and flow rate are different, by one of: at least about 2%, at least
about 5%, and at least about 10%, in all of the line segments.
According to an eleventh aspect, there is provided the method of
any one of aspects 1-10, wherein the cooling fluid is directed
annularly about the laser beam toward the glass sheet.
According to a twelfth aspect, there is provided an apparatus,
comprising:
a support table operating to support a glass sheet of about 0.2 mm
or less in thickness, the glass sheet having a defined cutting line
including at least one non-straight portion of a radius of less
than about 20 mm, where the non-straight portion of the cutting
line is divided into a plurality of sequential line segments, and
where the cutting line defines a desired shape of a glass
substrate;
a device operating to score the glass sheet to produce an initial
flaw;
a laser source operating to apply a laser beam to the glass sheet
starting at the initial flaw and continuously moving the laser beam
and the glass sheet relative to one another along the cutting line
to elevate a temperature of the glass sheet at the cutting
line;
a source of cooling fluid operating to apply a cooling fluid
simultaneously with the application of the laser beam, such that
the cooling fluid at least reduces the temperature of the glass
sheet in order to propagate a fracture in the glass sheet along the
cutting line;
a controller operating to vary one or more cutting parameters as
the laser beam moves from one of the plurality of line segments to
a next one of the plurality of line segments, wherein the one or
more cutting parameters include at least one of: (i) a power of the
laser beam, (ii) a speed of the movement, (iii) a pressure of the
cooling fluid, and (iv) a flow rate of the cooling fluid.
According to a thirteenth aspect, there is provided the apparatus
of aspect 12, wherein at least one of:
the laser beam is substantially circular having a diameter of the
laser beam is one of: (i) between about 1 mm to about 5 mm, and
(ii) between about 2 mm to about 4 mm; and
the laser beam is moderately non-circular having an aspect ratio of
less than about 2 and a diameter of less than about 5 mm.
According to a fourteenth aspect, there is provided the apparatus
of aspect 12 or aspect 13, wherein the controller operates to one
of:
vary the power of the laser beam such that the power level is
different in at least one of the line segments as compared to
others of the line segments; and
vary the power level of the laser beam such that the power level is
different in all of the line segments.
According to a fifteenth aspect, there is provided the apparatus of
any one of aspects 12-14, wherein the controller operates to one
of:
vary the speed of the movement of the laser beam relative to the
glass sheet such that the speed is different, by one of: at least
about 2%, at least about 5%, and at least about 10%, in at least
one of the line segments as compared to others of the line
segments; and
vary the speed of the movement of the laser beam relative to the
glass sheet such that the speed is different, by one of at least
about 2%, at least about 5%, and at least about 10%, in all of the
line segments.
According to a sixteenth aspect, there is provided the apparatus of
any one of aspects 12-15, wherein the controller operates to one
of:
vary at least one of the pressure and flow rate of the cooling
fluid such that at least one of the pressure and flow rate are
different, by one of: at least about 2%, at least about 5%, and at
least about 10%, in at least one of the line segments as compared
to others of the line segments; and
vary at least one of the pressure and flow rate of the cooling
fluid such that at least one of the pressure and flow rate are
different, by one of: at least about 2%, at least about 5%, and at
least about 10%, in all of the line segments.
According to a seventeenth aspect, there is provided the apparatus
of any one of aspects 12-16, wherein the cooling fluid is directed
annularly about the laser beam toward the glass sheet.
According to an eighteenth aspect, there is provided an apparatus,
comprising:
a glass substrate of about 0.2 mm or less in thickness that has
been laser cut from a source glass sheet,
wherein the glass substrate includes at least one non-straight
portion having a radius of less than about 20 mm, and an edge
strength of the at least one non-straight portion is greater than
about 150 MPa, and the at least one non-straight portion is not
strengthened by polishing.
According to a nineteenth aspect, there is provided the apparatus
of aspect 18, wherein the edge strength of the at least one
non-straight portion is greater than about 300 MPa.
According to a twentieth aspect, there is provided the apparatus of
aspect 18 or aspect 19, wherein the edge strength of the at least
one non-straight portion is greater than about 400 MPa.
According to a twenty first aspect, there is provided the apparatus
of any one of aspects 18-20, wherein the hackle size is less than
about 50% of the glass thickness.
* * * * *